Electro-mechanical energy conversion system having a permanent magnet machine with stator, resonant transfer link and energy converter controls

ABSTRACT

An electro-mechanical energy conversion system coupled between an energy source and an energy load comprising an energy converter device including a permanent magnet induction machine coupled between the energy source and the energy load to convert the energy from the energy source and to transfer the converted energy to the energy load and an energy transfer multiplexer to control the flow of power or energy through the permanent magnetic induction machine.

CROSS REFERENCE APPLICATION

This is a non-provisional patent application of provisional patentapplication Ser. No. 60/442,633 filed Jan. 23, 2003.

This invention was made with Government support under Contract NO.DE-FG36-03G013138 awarded by the Department of Energy. The Governmenthas certain rights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

An electro-mechanical energy conversion system including a permanentmagnet induction machine to selectively convert and transfer energy froman energy source and an energy load.

2. Description of the Prior Art

Seemingly limitless electro-mechanical systems and devices have beendevised to convert electrical energy to mechanical energy or vice versa.

In efforts to reduce dependency on fossil fuels, countless generatorsystems to convert mechanical to electrical energy including variouswind power systems or wind turbines have been developed. Such systemsgenerally include a shaft-mounted turbine to drive an electricalgenerator. To operate the generator at optimum speed for maximum poweroutput, the wind turbine must produce a relatively constant torque orspeed despite changes in wind speed and wind direction. Generally, thepitch of the turbine blades is varied to regulate the torque orresultant speed. Unfortunately, such pitch angle control mechanisms arecomplex and costly to manufacture, maintain and repair.

Moreover, such energy conversion systems using variable speed windturbine generators to provide the source of energy to utility powergrids require a matched constant output frequency at preferably optimumpower output. Thus, the variable frequency AC from such turbinegenerators must be converted to a constant frequency AC for use by theutility power grid. Generally, this conversion can be accomplishedthrough an intermediate conversion to DC by a rectifier and subsequentinversion to fixed-frequency AC by means of an inverter. Unfortunately,such systems are inefficient, relatively expensive, difficult tomaintain operation and relatively unreliable as an electricity source.

U.S. Pat. No. 5,028,804 discloses an energy conversion generation systemto receive energy from a resource and convert the energy into electricalpower for supply to a polyphase electrical power grid operating at asystem frequency. The controller establishes a reference signal, thenprocesses the sensor signal with the reference signal to produce acontroller signal. The converter produces the excitation power at anexcitation frequency in response to the controller signal so as toincrease the ratio of the electrical power output to the resource energypower input received by the prime mover.

U.S. Pat. No. 4,490,093 describes a windpower system comprising asupport and a turbine having a shaft rotatively mounted to the support.The turbine has variable pitch blades controlled by the differentialmotion of a rotary control shaft coaxial with the turbine shaft and theturbine shaft so that the blade pitch can be varied by a stationarymotor without requiring any slip rings or other such wear-pronecouplings. In the event of a power failure, rotary motion of the controlshaft is prevented so that the turbine blades are feathered solely dueto the force developed by the rotating turbine. When the turbine is usedto generate electrical power an induction generator is coupled to theturbine shaft. The shaft speed is indicative of generator output power.Thus, generator speed is monitored and used to control the pitch of theturbine blades so as to maintain generator output power at the maximumvalue when wind speed is below the machine's rated wind speed and nomore than rated output power when wind speed exceeds rated wind speed.

U.S. Pat. No. 4,426,192 teaches a method and apparatus for controllingwindmill blade pitch. The pitch of the turbine blades is based on adual-deadband control strategy. If the current turbine speed isdetermined to be outside of a relatively wide deadband, action is takento correct the speed by changing blade pitch. If the current speed iswithin the relatively wide deadband, then the average of the turbinespeed over an interval is compared with a relatively narrow deadbandwithin the wider deadband. Action is then taken to change the bladepitch if the average speed is outside the narrow deadband. In this way,wide excursions of turbine speed are corrected promptly, but thefrequency of control actions is minimized by requiring only the averagespeed to be kept within tight limits.

U.S. Pat. No. 6,137,187 relates to a variable speed system such as awind turbine comprising a wound rotor induction generator, a torquecontroller and a proportional, integral derivative (PID) pitchcontroller. The torque controller controls generator torque using fieldoriented control, and the PID controller performs pitch regulation basedon generator rotor speed

U.S. Pat. No. 5,225,712 shows a wind turbine power converter thatsmooths the output power from a variable speed wind turbine to reduce oreliminate substantial power fluctuations on the output line. The powerconverter has an AC-to-DC converter connected to a variable speedgenerator that converts wind energy to electric energy, a DC-to-ACinverter connected to a utility grid, and DC voltage link connected toan electrical energy storage device such as a battery or a fuel cell. Anapparatus and method for controlling the instantaneous current flowingthrough the active switches at the line side inverter to supply reactivepower to the utility grid is also disclosed. The inverter can controlreactive power output as a power factor angle, or directly as a numberof VARs independent of the real power. Reactive power can be controlledin an operating mode when the wind turbine is generating power, or in astatic VAR mode when the wind turbine is not operating to produce realpower. To control the reactive power, a voltage waveform is used as areference to form a current control waveform for each output phase. Thecurrent control waveform for each phase is applied to a currentregulator which regulates the drive circuit that controls the currentsfor each phase of the inverter. Means for controlling thecharge/discharge ratio and the regulating the voltage on the DC voltagelink is also disclosed.

U.S. Pat. No. 5,028,804 relates to an energy conversion generationsystem to receive energy from a resource and convert the energy intoelectrical power for supply to a polyphase electric power grid operatingat a system frequency. A prime mover driven by the resource energy and aconverter such as a power electronic converter produces excitation powerfrom power received from a converter power source. A brushlessdoubly-fed generator having a rotor with rotor windings and a statorwith stator windings comprises a first and second polyphase statorsystem. The rotor is driven by the prime mover. The first stator systemsupplies the electrical power to the grid, and the second stator systemreceives the excitation power from the converter. A sensor senses aparameter of the electrical power output supplied to the grid andproduces a sensor signal corresponding to the sensed parameter. Acontroller controls the converter in response to the sensor signal.

U.S. Pat. No. 4,523,269 discloses a DC to N phase AC converter, a DCsource having first and second terminals for deriving equal amplitudeopposite polarity DC voltages, a series resonant circuit, and N outputterminals, one for each phase of the converter. The series resonantcircuit is selectively connected in series with the first and secondterminals and the N output terminals for an interval equal to one halfcycle of the resonant circuit resonant frequency, so that current flowsbetween a selected one of the first and second terminals and theresonant circuit and a selected one of the N output terminals during theinterval. The resonant circuit current is zero at the beginning and endof the interval. A capacitor shunting each of the output terminals has avalue relative to the capacitance of the series resonant circuit suchthat the voltage across each output terminal remains approximatelyconstant between adjacent exchanges of energy between the resonantcircuit and the output terminal. The selective connection is in responseto a comparison of the actual voltage across each of the N outputterminals and a reference voltage for each of the N output terminals.The comparison controls when the flow of current between the selectedfirst and second terminals and the selected output terminal via theresonant circuit begins. The frequency of the AC voltage developedacross the N output terminals is much less than the resonant frequencyof the circuit.

Despite these systems, there remains a need for an efficient, reliablevariable speed energy conversion system.

SUMMARY OF THE INVENTION

The present invention relates to an electro-mechanical energy conversionsystem to selectively convert and transfer energy from an energy sourceto an energy load and an energy transfer multiplexer to selectivelycontrol the direction of power or energy flow through the energytransfer multiplexer to control the operation of the electro-mechanicalenergy conversion system.

The electro-mechanical energy conversion system may comprise a motor todrive a pump, fly wheel, or other such device or a generator to power anelectrical power grid or an electrical load.

For example, the electro-mechanical energy conversion system of thepresent invention comprises a permanent magnet induction machine toconvert wind energy into an electrical power output to a polyphaseelectric power grid operating at a system frequency comprising avariable speed generation system such as a turbine for converting thewind energy into mechanical energy and a generator coupled to theturbine to drive the rotor to create power in the stator to supplyelectrical power to the power grid. The generation system also includescontrol means for varying the rotor speed in response to the poweroutput and the wind energy to increase the ratio of the electricaloutput power to the wind energy input.

The electro-mechanical energy conversion system operates at highefficiency regardless of variable resource conditions by controlling therotor speed. Thus, the electro-mechanical energy conversion system canoperate at substantially reduced rating. Thus, the equipment andoperating costs are significantly lower than those of existing systems.

These and other objects, features and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and object of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1A is a block diagram of the energy transfer multiplexer of thepresent invention.

FIG. 1B is a block diagram of the electro-mechanical energy conversionsystem of the present invention.

FIG. 2A is a rotor voltage/rotor frequency curve for theelectro-mechanical energy conversion system for the present inventioncontrolling a doubly fed induction machine.

FIG. 2B is a mechanical input power/rotation rate curve for theelectro-mechanical energy conversion system of the present inventioncontrolling a doubly fed induction machine.

FIG. 2C is a rotor power/rotation rate curve for the electro-mechanicalenergy conversion system of the present invention controlling a doublyfed induction machine.

FIG. 3A is a block diagram of the electro-mechanical energy conversionsystem of the present invention implemented with a doubly fed inductionmachine and mechanical energy source.

FIG. 3B is a block diagram of the electro mechanical energy conversionsystem of the present invention implemented with a permanent magnetgenerator or machine and mechanical energy source.

FIG. 3C is a block diagram of an electrical to electrical energyconversion system of the present invention.

FIG. 4 is a topological schematic of the energy transfer multiplexer orenergy transfer section of the electro-mechanical energy conversionsystem of the present invention implemented with IGBT switches.

FIG. 5 is a circuit diagram of the energy transfer multiplexer or energytransfer section of the electro mechanical-energy conversion system ofthe present invention implemented with IGBT switches.

FIG. 6 is a schematic of the drivers or controlled power switches of theenergy transfer section of the electro-mechanical energy conversionsystem of the present invention implemented with IGBT switches.

FIG. 7 is a schematic of the sensors of the energy transfer multiplexeror energy transfer section of the electro-mechanical energy conversionsystem of the present invention implemented with IGBT switches.

FIG. 8 is a schematic the drivers or controlled power switches of theenergy transfer multiplexer or energy transfer section of theelectro-mechanical energy conversion system of the present inventionimplemented with SCR switches.

FIG. 9 shows an IGBT power switch or driver of the electro-mechanicalenergy conversion system of the present invention for the IGBT switches.

FIG. 10 shows a SCR power switch or driver of the electro-mechanicalenergy conversion system of the present invention for the SCR switches.

FIG. 11 shows the initial or starting polarity and the final polarity ofthe capacitor potential for the plurality of switches or control pointsof the energy transfer multiplexer or electro-mechanical energyconversion system of the present invention and the associated pluralityof the differential voltage, _(I)Δ_(O) between the input E₁ and outputE₀ potential.

FIG. 12 depicts various electrical charge states on the bi-directionalresonant link of the energy transfer multiplexer or electro-mechanicalenergy conversion system of the present invention.

FIG. 13 shows the informational or decision flow and control logic forswitching states of the first and second plurality of switches or energytransfer control points of the energy transfer multiplexer orelectro-mechanical energy conversion system of the present invention.

FIG. 14 shows a sinusoidal energy reference curve of theelectro-mechanical energy conversion system of the present invention.

FIGS. 15 through 17A and 17B show the process of pre-charging theshuttle or resonant capacitor of the energy transfer multiplexer orelectro-mechanical energy conversion system of the present invention.

FIG. 18 shows the energy transfer through the bi-directional resonanttransfer link of the energy transfer multiplexer or electro-mechanicalenergy conversion system of the present invention where the current flowor charge transfer is from E₁ to E₀ (left to right) equation.

FIG. 19 shows the energy transfer through the bi-directional resonanttransfer link of the energy transfer multiplexer or electro-mechanicalenergy conversion system of the present invention transferring energyfrom the load to the source and equation where the current flow orcharge transfer is from −E₀ to −E₁ (right to left).

FIG. 20 continues and completes the family of equations deriving thequantity of current transferred between the rotor and stator of theelectro-mechanical energy conversion system of the present invention.

FIG. 21 is a graphic depiction of the energy or power transfer of theenergy transfer multiplexer or electro-mechanical energy conversionsystem of the present invention.

FIG. 22 is another graphic depiction of the energy or power transfer ofthe energy transfer multiplexer or electro-mechanical energy conversionsystem of the present invention.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to an electro-mechanical energy conversionsystem including a permanent magnet induction machine to selectivelyconvert and transfer energy from an energy source to an energy load andan energy transfer multiplexer to selectively control the flow of energyfrom an energy source to an energy load.

The electro-mechanical energy conversion system of the present inventionmay be configured to operate as a generator or motor. As a generator,the electro-mechanical energy conversion system can convert mechanicalenergy from wind turbines, hydro turbines, steam turbines, internalcombustion engineers, fly wheels and the like to generate electricalenergy to power an electrical power grid, rural power, electric boats,industrial pumps and the like.

The electrical energy can also be converted and stored in the form ofhydrogen storage, batteries or compressed air for future use. Likewise,as a motor, the electro-mechanical energy conversion system can convertelectrical energy from an electrical power source to power a wide rangeof mechanically driven or powered devices or systems such as electricboat drives, traction drives, pumps and fans. Of course, there is noknown limit as to the application of the electro-mechanical energyconversion system either as a generator or motor.

The present invention can include a selectively controlledbi-directional inverter and an energy converter device comprising thepermanent magnet induction machine to create a sinusoidal currentsource/sink.

When the electro-mechanical energy conversion system operates with adoubly fed induction generator, a variable frequency/amplifier 3 phaseAC excitation current is fed to the rotor winding to generate a rotorelectrical excitation frequency. Power is selectively fed to or from therotor windings to transfer substantially constant frequency, constantamplitude power through the air gap to the stator windings.Specifically, rotor electrical excitation frequency is either added toor subtracted from the rotor mechanical (shaft speed): frequency togenerate a substantial constant 3 phase AC power output on the statorwinding.

Since the bi-directional inverter operates either as a sinusoidalcurrent source or as a sinusoidal current sink, the electro-mechanicalenergy conversion system as described more fully hereinafter generates asinusoidal current at the desired frequency or accepts a sinusoidalcurrent at a given frequency thereby selectively transferring energy ineither direction. This significantly expands the stability of theoperating region of a doubly fed induction machine with a substantial30% to 45% reduction in the required power level at the rotor winding ascompared to equivalent pulse width modulation devices. This powerreduction coupled with the reduction in the need for additional harmonicfiltering reduces the cost of bi-directional compared to an equivalentPWM converter by about 1 cent per watt of delivered grid power; i.e.$30,000 for a 3×10⁶ watt system. In other words, the increased stabilityof the induction machine and increased operating frequency range allowsa lower converter maximum power level with attendant reduced costs.

In addition, by utilizing a bi-directional sinusoidal current, theincreased stability coupled with the removal of the “PWM required”filter, improves on the design requirements for the mechanicalcomponents by reducing the number of components required or bydecreasing the ratings of some of the components. The faster operatingresponse improves the elasticity of the mechanical generator drivetrain. This increased compliance, coupled with sinusoidal currentwaveform reducing torque ripple prolongs the operating life of thevarious mechanical components.

Moreover, the increased stability on the system also permits a change inthe gear ratio and therefore the rotor frequency band above and belowthe 60 Hertz operating point from ±20 Hertz to +32 Hertz, −8 Hertz. Thisreduces the required power level of the energy converter and permitsadditional mechanical power source capture and improved generatorperformance at the high frequency high power point. Thus the maximummechanical power input occurs at 68 Hertz reduced from 80 Hertzassociated with typical variable speed input energy sources. As aresult, the present invention can be effectively implemented with a fourpole configuration rather than a six pole configuration with anattendant reduction in generator cost of about 30%.

Further, this 12 Hertz or 720 revolutions per minute reduction in therate of rotor rotation reduces not only the mechanical stress but alsoincreases maximum power available from the generator.

These aspects of the present invention provide substantial design andoperational flexibility with attendant fabrication and operatingsavings.

As shown in FIG. 1A, the energy transfer multiplexer comprising abi-directional resonant inverter generally indicated as 2 including afirst bank or plurality of switches or energy transfer control pointsgenerally indicated as 4 and a second bank or plurality of switches orenergy transfer control points generally indicated as 6 operativelycoupled by a series resonant transfer link generally indicated as 8 toselectively control the direction of power or energy flow between thefirst and second bank or plurality of switches or energy transfercontrol points 4 and 6 to control the operation of an electro-mechanicalenergy conversion system in response to a plurality of predeterminedconditions or parameters as described more fully hereinafter. Althoughthe operation of the energy transfer multiplexer 2 is described inassociation with the electro-mechanical conversion system 10, the energytransfer multiplexer 2 is useful in other applications.

As shown in FIG. 1B, the electro-mechanical energy conversion system 10comprises an energy converter device such as a permanent magnetinduction machine or doubly fed induction machine as described morefully hereinafter coupled between an energy source 12 and the energyload 14 to convert the energy from the energy source 12 and an transferthe converted energy to the energy load 14.

As shown in FIG. 3A, the electro-mechanical energy conversion system 10comprises an energy converter device generally indicated as 16 coupledbetween the input energy source 12 and the output energy load 14 toconvert the energy from the input energy source 12 from one form ofenergy to another and to transfer the converted energy to the outputenergy load 14 and an energy conversion and transfer control 18 toselectively control the energy converted from the input energy source 12and transferred to the output energy load 14 in response to a pluralityof predetermined conditions or parameters.

As shown in FIG. 3A, the energy converter device 16 includes an energyconverter section or device 20 comprising a doubly fed induction machinehaving a rotor 22 and stator 24 to selectively convert the energy fromthe input energy source 12 and to selectively transfer the convertedenergy to the output energy load 14 and an energy transfer section orenergy transfer multiplexer 26 coupled to the energy conversion sectionor device 20 comprising the doubly fed induction machine to selectivelytransfer energy between the rotor 22 and the stator 24 and to feed theconverted energy to the output energy load 14 as described more fullyhereinafter.

The energy conversion and transfer control or energy management system18 comprises an energy converter control 28 to control the operation ofthe energy transfer device or energy transfer multiplexer 26 and asource/load control 30 to control the operation of the input energysource 12 and output energy load 14 with respect to the energy converterdevice 16.

FIG. 3A depicts the electro-mechanical energy conversion system 101 asgenerator with a wind turbine device as the input energy source 12. Asdescribed more fully hereinafter, since the wind turbine device is avariable speed energy source, the energy transfer device 26 and energyconverter control 28 of the energy conversion and transfer control 18control the electrical excitation of the windings of the rotor 22 of thedoubly fed induction machine 20 to generate three phase power on thestator 24 matching the frequency of the three phase power of the stator24 with the AC frequency of the output energy load 14.

FIG. 3B depicts the electro-mechanical energy conversion system 10wherein the energy converter section or device 20 comprises a permanentmagnet induction machine in place of the doubly fed induction machine 20depicted in FIG. 3A. Otherwise, the various components of theelectro-mechanical energy conversion system 10 are virtually the same.

FIG. 3C depicts an electrical to electrical energy conversion system 10using electrical power as the input energy source 12. The energytransfer multi-plexer shown in FIGS. 3A, 3B and 3C respectively aresimilar in function and operation as described hereinafter

FIGS. 4 through 7 show the energy transfer device or energy transfermultiplexer 26 implemented through the use of IGBT switches; while, FIG.8 shows the energy transfer device 26 implemented through the use of SCRswitches.

As best shown in FIGS. 4 and 5, the energy transfer device 26 comprisesa plurality of rotor energy transfer control elements or switchesgenerally indicated as 102 and a plurality of stator energy transfercontrol elements or switches generally indicated as 104 operativelycoupled in energy transfer relationship by a bi-directional resonanttransfer link generally indicated as 106 and an isolation element orcomponent generally indicated as 108.

The energy transfer multiplexer 26 may include the isolation element orcomponent 108 as shown in FIGS. 4 through 8 or may be implementedwithout the isolation element or component 108 are shown in FIG. 1A. Forexample, when the energy transfer multiplexer 26 is used with a doublyfed induction machine the rotor winding is already isolated from thestator winding obviating the necessity of an isolation transformer.

The plurality of rotor energy transfer control elements or switches 102comprises an IGBT switch 110 coupled to each phase A, B, C of the rotor22 of the doubly fed induction machine by a corresponding conductor orline 112 shunted to ground by a corresponding shunt capacitor 114.Similarly, the plurality of stator energy transfer control elements orswitches 104 comprises an IGBT switch 116 coupled to each phase a, b, cof the stator 24 of the doubly fed induction machine 20 by acorresponding conductor or line 118 connected to corresponding sliprings 119 and shunted to ground by a corresponding shunt capacitor 120.The bi-directional resonant transfer link 106 comprises a seriesresonant inductor 122 and resonant capacitor 124; while, the isolationelement or component 108 comprises a transformer generally indicated as126 coupled between the bi-directional resonant transfer link 106 andthe plurality of energy transfer control elements or switches 104.

The energy transfer device 26 further includes a first local groundenergy transfer control element or switch 128 coupled or connectedbetween one side of the resonant link 8 to ground and a second localground energy transfer control element or switch 130 coupled orconnected between the opposite side of the resonant link 8 and ground12.

As shown in FIG. 6, the operation in energy transfer control elements orIGBT switches 110, 116, 128 and 130 are controlled by a correspondingdriver 132 coupled to the energy conversion and transfer control 18 by acorresponding driver conductor or line 134. Energy transfer controlelements or IGBT switches 110, 116, 128 and 130 and driver 132connections are shown in detail in FIG. 9.

FIG. 7 shows a plurality of operating parameters or condition sensors tosense and feed real time current and voltage values or data to theenergy converter control 28 of the energy conversion and transfercontrol 18.

Specifically, the rotor phase current for each phase A, B, C of therotor 22 of the doubly fed induction machine 20 is monitored or sensedat corresponding sensor point 136 on corresponding conductors or lines112 and fed to the energy converter control 28 of the energy conversionand transfer control 18 by corresponding conductors or lines 137; while,the stator phase current for each phase a, b, c of the stator 24 of thedoubly fed induction machine 20 are monitored or sensed by acorresponding current sensor 138 and fed to the energy converter control28 of the energy conversion and transfer control 18 by correspondingconductors or lines 139. Current through the primary and secondarywindings of the transformer 126 are monitored or sensed by atcorresponding sensor points 140 and 142 respectively and fed to theenergy converter control 28 of the energy conversion and transfercontrol 18 by corresponding conductors or lines 141 and 143respectively. In the event no transformer 126 or isolation device isused, the line current is monitored or sensed.

The rotor phase voltage for each phase A, B, C of the rotor 22 of thedoubly fed induction machine 20 is monitored or sensed at sensor points138 on corresponding conductors or lines 112 and fed to the energyconverter control 28 of the energy conversion and transfer control 18 bycorresponding conductors or lines 144; while, the stator phase voltagefor each phase a, b, c of the stator 24 of the induction machine 20 aremonitored or sensed at corresponding sensor points 138 or equivalent oncorresponding conductors or lines 118 and fed to the energy convertercontrol 28 of the energy conversion and transfer control 18 bycorresponding conductors or lines 146. The stator common voltage and thefundamental resonant capacitor voltages on opposite sides of theresonant choke 122 and the resonant capacitor 124 are monitored orsensed at corresponding sensor points 148, 150 and 152 respectively andfed to the energy converter control 28 of the energy conversion andtransfer control 18 by corresponding conductors or lines 154, 156 and158 respectively.

The energy transfer device 26 implemented with SCR switches is similarin topology, sensing and control. As shown in FIG. 8, the energytransfer device 26 using the SCR switches comprises a plurality of rotorenergy transfer control elements or switches generally indicated as 202and a plurality of stator energy transfer control elements or switchesgenerally indicated as 204 operatively coupled in energy transferrelationship by a bi-directional resonant transfer link generallyindicated as 206 and an isolation element or component generallyindicated as 208. The plurality of rotor energy transfer controlelements or switches 202 comprises an SCR switch 210 coupled to eachphase A, B, C of the rotor 22 of the doubly fed induction machine 20 bya corresponding conductor or line 212 shunted to ground by acorresponding shunt capacitor (not shown). Similarly, the plurality ofstator connected energy transfer control elements or switches 204comprises an SCR switch 216 coupled to each phase a, b, c of the statorwindings 24 of the doubly fed induction machine 20 by a correspondingconductor or line 218 shunted to ground by a corresponding shuntcapacitor (not shown). The bi-directional resonant transfer link 206comprises a series resonant inductor 222 and resonant capacitor 224;while, the isolation element or component 208 comprises a transformergenerally indicated as 226 coupled between the bi-directional resonanttransfer link 206 and the plurality of rotor energy transfer controlelements or switches 204. The energy transfer device 26 further includesa first local ground energy transfer control element or switch 228 and asecond local ground energy transfer control element or switch 230coupled between ground and opposite sides of the bi-directional resonanttransfer link 206. A reset control comprising an IGBT switch 231 coupledto the resonant inductor 222 by a secondary winding 233 is used to resetthe SCR switches 210 and switch 216 as described more fully hereinafter.

As shown in FIG. 8, the operation of the SCR switch energy transferinverter is controlled by the energy transfer control elements or SCRswitches 210, 216, 228 and 230 and the commutating switch 231 are turnedon by drivers 232 controlled through lines 234 from controller 28 andcommutated off by the reset control IGBT switch 231 controlled by acorresponding driver 132 coupled to the controller 28 of the energyconversion and transfer control 18 by a corresponding driver conductoror line 134.

A plurality of operating parameters or condition sensors used to senseand feed real time current and voltage values or data to the energyconverter control 28 of the energy conversion and transfer control 18for the SCR switch implementation is virtually the same as that shown inFIG. 7 for the IGBT switches implementation except for the SCR resetswitch 231 to reset the SCRs after each energy transfer.

As previously mentioned, the electro-mechanical energy conversion system10 can operate with various prime movers as a generator. Such primemovers require resource energy adjustment means responsive to acontroller signal for controlling or limiting the resource energy fromthe input energy source 12 to the stator 24 of the electro-mechanicalenergy conversion system 10. For example, a hydro turbine generally hasa hydro inlet and gate means such as a gate for closing the hydro inletin response to a gate position signal. Similarly, a steam turbinegenerally has variable position inlet gate valves that open and close tocontrol the amount of steam received by the turbine. Wind turbinestypically have adjustable blades with an adjustable pitch angle that isvaried to control the force of the wind received by the turbine blades.Solar energy power generation systems generally have adjustable solarpanels or mirrors, which may be adjusted to vary the angle of incidenceof the solar rays on the panels or mirrors.

More particularly, when used with a hydro turbine, the resource energyadjustment comprises a gate means for dosing the hydro inlet of thehydro turbine in response to the turbine controller signal. The turbinecontroller signal comprises a gate position signal. A turbine efficiencymaximizer means receives and processes the head sensor signal and thegate position signal to produce the hydro turbine efficiency outputsignal. U.S. Pat. No. 5,028,804 discloses such a generator controlsystem. For a wind turbine, a turbine controller produces a wind turbinecontroller signal that comprises a blade pitch adjustment signal. A windturbine including adjustable blade with variable pitch angles, theresource energy adjustment means comprising means for adjusting thepitch angle of the blades in response to the blade pitch adjustmentsignal. A wind turbine efficiency maximizer receives and processes thewind speed sensor signal and the blade pitch adjustment signal toproduce a wind turbine efficiency output signal U.S. Pat. No. 6,137,187shows such a variable speed wind turbine generator control system.

As previously stated, FIG. 3A depicts the implementation of theelectro-mechanical energy conversion system 10 using wind power as theinput energy source 12 to generate electrical energy transferred to anoutput energy load on grid 14. When operating as a wind poweredgenerator, the input energy source 12 comprises a wind driven propeller310 coupled to the rotor 22 through a gear assembly or other mechanicalcoupling mechanism 312 and an output shaft 314. As describedhereinafter, the energy converter control 28 of the electro-mechanicalenergy conversion system 10 compensates for changing wind speed anddirection to supply power to the output energy load or power grid 14 ata substantially constant 60 Hertz output from the stator 24. This isaccomplished by electrically exciting the rotor windings such that therotor mechanical frequency and rotor electrical excitation frequency aretheoretically equal to substantially 60 Hertz. The resultant 60 Hertzenergy or power on the rotor 22 is transferred across the air gap of thedoubly fed induction machine 20 to the stator 24 to be supplied to thegrid 14 at substantially 60 Hertz through a switch 316. While a threephase grid is shown, the electro-mechanical energy conversion system 10may be implemented for use with a single phase load.

The operation of the energy transfer multiplexer 26 as describedhereinafter with either a doubly fed induction machine or a permanentmagnetic induction machine is essentially the same. However, as show inFIG. 3A, when used with a doubly fed induction machine, the energytransfer multiplexer 26 is coupled between the windings of the woundmotor 22 and energy converter section or device 20 and the stator 24 ofthe energy converter section or device 20 and the energy load 14 totransfer energy bi-directionally through the energy transfer multiplexer26 to compensate for variations in the input energy source 12 to createor generate a virtual rotor frequency of 60 Hertz. On the other hand, asshown in FIG. 3B, when used with a permanent magnetic induction machine,the energy transfer multiplexer 26, isolated from the energy source 12,is coupled between the stator 24 of the energy converter section ordevice 20 (permanent magnet) and the load 14 to transfer the variableenergy supply from the energy source 12 through the rotor 22 and stator24 of the energy converter section or device 20 to the load. The energytransfer multiplexer 26 receives variable frequency energy signals fromthe stator 24 and compensates for these varying frequency energy signalsto feed a substantially constant frequency of 60 Hertz. In short, in thedoubly fed induction machine, the input or output frequency of the rotorwindings or the rotor 22 of the energy transfer multiplexer 26 isvariable and the output frequency of the stator 24 of the energyconverter section or device 20 is substantially constant. In comparison,in the permanent magnet induction machine, the output frequency of thestator 24 of the energy converter section of device 20 fed to the energytransfer multiplexer 26 is variable; while the output for the energytransfer multiplexer 26 fed to the energy load 14 is substantiallyconstant.

The energy transfer multiplexer 26, when used to control a variablespeed permanent magnetic generator, has numerous operational and costadvantages.

Specifically, a permanent magnetic generator powered by a wind turbineat variable rotational speed outputs electrical energy with a sinusoidalwave form that varies in both frequency and voltage amplitude.Accordingly, for a 3 phase permanent magnetic generator, the energytransfer multiplexer electrical configuration has four input switches, 3phase switches and an input ground switch, connected through a seriesresonant circuit to four output phase switches, 3 output switches and anoutput ground switch. Operation of the input phase switch in conjunctionwith the output ground switch allows the energy transfer multiplexer tofunction as a “charge pump” thereby allowing electrical charge to betransferred from a lower voltage to a higher voltage.

In contrast, pulse width modulation requires massive, expensive, lowfrequency DC inductors to obtain significant voltage gain.

Another advantage is the ability to actively, selectively andsimultaneous control both the input and output power factor.

The energy transfer multiplexer selectively controls the four input andfour output switches to allow varying size packets of charge to betransferred from the variable time varying input phase voltage to thevariable time varying output phases. Accordingly, greater current flowfor leading power factor or smaller current flow for lagging powerfactor can be obtained at a given value voltage of the AC waveforms.

In addition, the energy transfer multiplexer 26 is a bi-directionalpower flow allowing wind turbines to spin-up or start at very low windspeed by transferring power from the 3 phase grid to the permanentmagnet generator as a permanent magnet motor.

The energy transfer multiplexer 26 is a symmetrical network thatselectively processes power flow in either direction.

An advantage of electro-mechanical energy conversion system 10 with theenergy transfer multiplexer 26 as opposed to pulse width modulation(PWM) power conversion, for wind turbines for both permanent magnetgenerators and doubly fed wound rotor machines is the large systembandwidth. The energy transfer multiplexer allows direct AC to ACconversion without utilizing an intermediate DC link; the benefits ofenergy transfer multiplexer resonant link for direct AC to AC conversionwithout a DC link include:

-   -   System soft-start with current in rush control, when the        permanent magnet machine is operating as a generator or as a        motor.    -   Very low windspeed start-up because of the energy transfer        multiplexer property of variable voltage gain    -   The energy transfer multiplexer symmetrical configuration allows        the permanent magnet generator to spin-up the windturbine at        zero windspeed utilizing the grid power.    -   Rapid transient response allowing improved system stability;        energy transfer multiplexer does not require high current-low        frequency chokes that cause time delay in the in the system        response.    -   Rapid, almost instantaneous, shut-down because both the input        and output phase switches are opened after each charge transfer        at zero current and if not reclosed constitute an automatic        shutdown.    -   Improved system compliance because as the rapid transient        response, soft-start and substantially instantaneous shut-down.

Finally, the compact design of permanent magnet generators allowsrelatively higher speed operation. The AC to DC rectification requiredfor the PWM DC link is limited by inductance at high power levels athigher generator frequencies. With no requirement for a DC link, energytransfer multiplexers samples the AC sinusoidal wafeform with discretesmall-duration (typically 20 ms-40 ms) time intervals that with optimumphase to ground by pass capacitors allow the generator to, operate withlow distortion sinusoidal current and voltage waveforms at near unitypower factor.

The eight switch symmetrical (4 switch resonant link) configurationincludes a maximum of power processing system functionality; high gain,high bandwidth, high frequency, high efficiency, bi-directional powerprocessing with soft-start, rapid shut-down and dual PF control.Further, the energy transfer multiplexer low distortion sinusoidalwaveform operation inherently minimizes EMI, physical size and weightbecause unlike PWM, large high current low frequency DC magnetic filtersare not required in energy transfer multiplexer power processors.Lastly, the energy transfer multiplexer symmetrical 8-switch powernetwork, operating by transferring individual packets of electricalcharge, represents a digitally controlled generic power processorapplicable to all types of rotating electromagnetic machines.

In summary, a comparison of pulse width modulation and energy transfermultiplexer configurations and operating parameters shows that the solidstate components, semiconductors and diodes, with other electrostaticand resistive components are roughly equivalent. Even the heat sinks(efficiency) and wiring requirements are about the same complexity. Theunique advantage of energy transfer multiplexer in wind turbine powerprocessing relates to:

-   -   size—energy transfer multiplexer do not require large expensive        robust magnetic filters;    -   weight—no magnetic filters;    -   performance        -   a) high speed more compact generator,        -   b) low windspeed power through-put (constant conversion            efficiency)        -   c) broad speed (operational frequency) range with sufficient            voltage gain at the lower end of the frequency range    -   soft-start;    -   rapid shut-down, no stored energy    -   wide bandwidth, transient control

For wind turbines with permanent magnet generator energy transfermultiplexer, the reduction in annual cost of power (a function of annualaverage wind speed) may be 10% to 40%.

For wind turbines with DFIM (large turgines) with energy transfermultiplexer, the initial cost of the power electronics is calculated tobe reduced by 20% to 50% relative to pulse width modulationimplementation.

As described in U.S. Pat. No. 6,137,187, various operating parameters orconditions associated with the input energy source 12 such as windconditions, blade pitch, blade rotational speed and torque may besupplied to or calculated by the source/load control 30 to control theoperation of the mechanical input such as blade pitch through feed backloops depicted generally as 318. Control signals and sensor signals arefed between energy converter control 28 and source/load control 30through cable or lines 320 and between energy transfer device 26 andenergy converter control 28 through cables or lines 322.

The energy converter control 28 controls the operation of the energytransfer device 26 to maintain the effective frequency of the rotor 22,mechanical frequency plus or minus winding excitation frequency, atsubstantially 60 Hertz through the operation of the bi-directionalresonant transfer link 106 by selecting the switching states of therotor energy transfer control elements or IGBT switches 102 or SCRswitches 202 and the stator energy transfer control elements or IGBTswitches 104 or SCR switches 204 to control the transfer of excitationenergy to and from the rotor windings.

The switching states of IGBT switches 110, 116, 128 and 130 or SCRswitches 210, 216, 118 and 230 and IGBT switch 231 of the correspondingenergy transfer device 26 are selectively controlled by the convertertransfer control logic of the micro-controller or microprocessor in theenergy converter control 28 of the energy conversion and transfercontrol 18 to adjust excitation of the rotor windings of the doubly fedinduction machine 20 through three phase slip rings generally indicatedas 324 to compensate for changes or variations in the mechanical inputconditions such as frequency and power level.

The various system currents and voltages previously described are sensedand fed to the energy converter control 28. At the same time, themechanical rotor speed or rotational rate is measured. If the mechanicalrotor speed or rotational rate is substantially 60 Hertz, power orexcitation energy is neither added to nor subtracted from the rotorwindings. However, if the mechanical rotor speed or rotation rate isgreater than or less than substantially 60 Hertz, power or excitationenergy is subtracted from or added to the rotor windings.

As shown in FIG. 2A, when the mechanical rotor speed or rotation rate ofthe rotor 22 is greater than substantially 60 Hertz, the doubly fedinduction machine 20 operates as a current sink drawing power from therotor windings to compensate for the mechanical rotation over-speed ofthe rotor 22 to generate a magnetic stator (output) frequency ofsubstantially 60 Hertz; the mechanical rotor speed (frequency) lessrotor winding excitation frequency at the correct corresponding voltage,amplitude form a straight line curve shown on the right side of FIG. 2A.Conversely, when the mechanical rotor speed or rotational rate of therotor 22 is less than substantially 60 Hertz, the doubly fed inductionmachine 20 requires as a current source feeding power into the rotorwinding to compensate for the mechanical rotational under-speed of therotor 22 to create a effective rotor speed (frequency) of substantially60 Hertz; the mechanical rotor speed (frequency) plus rotor windingexcitation magnetic frequency, at the corresponding voltage amplitude,also form the straight line phase curve shown on the left of FIG. 2A.

The micro-controller or microprocessor of the energy converter control28 generates reference curves corresponding to the compensating rotorpulse repetition frequency and corresponding power amplitude of thepower transferred between the rotor 22 and stator 24 to maintain theeffective rotational rate of the rotor 22 at substantially 60 Hertz. Theelectro-mechanical energy conversion system power output is shown inFIGS. 2B and 2C.

FIG. 11 shows the various possible switching configurations of the rotorswitches 102 or 202 and the stator switches 104 or 204. Specifically,any one of the three phase rotor switches 110 or 210 or the first groundswitch 128 or 228 can be closed or actuated at the same time with anyone of the stator switches 116 or 216 or the second ground energytransfer control element or switch 130 or 230 to control the transferenergy between the rotor 22 and the stator 24 as represented in FIG. 12.

As stated, the microprocessor or micro-controller of theelectro-mechanical energy conversion system 10 generates a referencecurve or sine wave for each phase of the doubly fed induction machine 20as shown in FIG. 14 in accordance with the substantially linearrelationship between the mechanical rotor speed or frequency and voltageor amplitude of the energy converter device 16 whether operating as acurrent source, 40 Hertz to 60 Hertz, or a current sink, 60 Hertz to 80Hertz as shown in FIG. 2A. The various values of the stator and rotorcurrents and voltages are sensed and fed to the micro-controller. Thecapacitor voltage are also sensed and fed to the microprocessor. Theseoperating parameters or conditions are compared with referenceappropriate curve dictated by the mechanical rotor speed and grid powerdemands to generate control signals to control drivers to actuate orenable switches 102 and 104 or 202 and 204. In addition, the SCRs areself commutative by the reset control IGBT switch 231.

The energy management system of the present invention comprises theenergy transfer multiplexer 2 coupled to the energy source 12 to receiveenergy therefrom and to the energy load 14 to feed energy thereto and asystem control coupled to the energy transfer multiplexer 2 to controlthe flow power to the energy load 14. As previously described, theenergy transfer multiplexer 2 power comprises the first plurality ofswitches or control points 4 coupled to the energy source 12 to receiveenergy therefrom and a second plurality of switches or control points 6coupled to the energy load 14 to feed energy thereto coupled by theresonant link 8 to transfer unrectified A/C signals therebetween and thesystem control comprising the plurality of sensors to monitor operatingconditions of the signal processing to control the operation of theenergy transfer multiplexer in response to the operating conditionswherein the plurality of sensors coupled between the logic section andthe first plurality of switches or control points, the second pluralityof switches or control points and the resonant link to sense the voltagelevels of each of the first plurality of switches or control points andeach of the second plurality of switches or control points and thevoltage level across the capacitor and to generate voltage level signalscorresponding to each voltage level and to feed the voltage levelsignals corresponding to each voltage level and to feed the voltagelevel signals to the logic section for processing and generate controlsignals fed to the switches or control points or sites as shown in FIG.13. The entire signal processing and signal generation is timedependent.

The energy management system or signal processing section comprisespower/phase management section, a polarity management section, a voltagemanagement section and a switch management section to receive operatingvoltage signals, compare the operating voltage signals withpredetermined voltage references and generate control signals when theoperating voltage signals exceed the predetermined voltage reference tocontrol the transfer of energy through the energy transfer multiplexer26.

Specifically, the voltage for each switch 110 and 116 or 210 and 216 issampled or interrogated to determine whether or not potential for phaseA, B, C on the rotor 22 and for phase a, b, c on the stator 24 arewithin a predetermined range or band on either side of the appropriatevoltage reference curve exemplified in FIG. 14. The actual voltagesmeasured as the various phases are compared in the power/phasemanagement section to determine if the corresponding phase voltage iswithin the predetermined reference-band. If-so, no-power is transferredinto or out of the rotor 22 for the time increment and phase sampled.

The operation of the energy transfer multiplexer 26 as depicted in FIGS.4 and 8, is best understood with reference to FIG. 13. In particular, ifenergy transfer is required, the polarity of charge across the resonantcapacitor 124, 224 is sensed by polarity management section andcorrected or reversed if necessary. To correct the polarity of thecharge on the resonant capacitor 124, 224, if necessary, both sides ofthe resonant link 106/206 are connected or coupled simultaneously tolocal ground by the first ground switch 128/228 and second ground energytransfer control element or switch 130/230 for one-half cycle of theresonant frequency. With the correct polarity for the output phaseconnection request, the resonant capacitor 124, 224 is connected betweenthe selected input switch 110, 210 phase A,B,C, or ground switch 128,228 and the selected output switch 116, 216 on phase a,b,c.

The voltage management section calculates and compares the final changeV_(CF) on the resonant capacitor 124/224 with a first predeterminedvoltage value such as three times the capacitor break down voltage 3E_(MAX) if the final charge V_(CF) is equal to or greater than the firstpredetermined voltage, then the resonant link 106/206 is connected toground through ground switch 128/228 and to the selected phase switch116/216 (indicated on FIG. 13 as G_(I)-E_(O)) to discharge the storedenergy on resonant capacitors 124/224 to provide a safety margin toprevent the voltage across the resonant capacitor 124/224 from exceedingthe breakdown voltage. If the final charge V_(CF) is less than the firstpredetermined, the initial charge V_(cs) on the resonant capacitor124/224 is compared to a second predetermined voltage value such as 1.5times the output voltage E_(O). If the initial charge V_(CS) is equal toor greater than the second predetermined voltage, then the resonant link106/206 is connected to ground though ground switch 128/228 and theselected output phase switch 116/216 (FIG. 13 as G_(I)-E_(O)). If theinitial charge V_(CS) is less than the second predetermined voltage, thesum of the selected input voltage E_(I) and the initial charge V_(CS) iscompared to the output voltage E_(O). If the sum of the input voltageE_(I) and initial charge V_(CS) is equal to or less than the outputvoltage E_(O), then the resonant link 116/216 is connected betweenselected input switch 110/210 and ground switch 130/230 to increase theentire charge V_(CS). If the sum of the input voltage E_(I) and initialcharge V_(CS) is greater than the output voltage E_(O), then theresonant link 116/216 is connected between E_(I) and E_(O) to completethe energy transfer between the energy source 12 and the energy load 14.

The switch management section generates output for resonance wait ordelay time.

In other words, with the correct polarity across the resonant capacitor124/224, when the V_(CF) is less than a predetermined multiple ofE_(MAX) and V_(CS) is less than a predetermined multiple of E_(O) andthe sum of E_(I) and V_(C) is greater than E_(O), the poled input phaseE_(I) supplies power or energy to the poled output phase E_(O) byclosing the corresponding switches; the resonance wait or delay time isto allow time for the resonant transfer before re-triggering the system.

On the other hand, with the correct polarity across the resonantcapacitor 124/224, when the V_(CF) is less than a predetermined multipleof E_(MAX) and V_(CS) is less than a predetermined multiple of E_(O) andthe sum of E_(I) and V_(c) is less than E_(O) the poled input phaseE_(I) is connected to G_(O) to increase the charge on the resonantcapacitor 124/224; this sequence may be repeated as indicated in FIGS.15 and 16B.

With the correct polarity across the resonant capacitor 124, 224, whenthe V_(CS) is greater than a predetermined multiple of E_(MAX) or theV_(CF) is greater than a predetermined multiple of E_(O), the poledoutput phase E_(O) is connected to G_(I) to discharge.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description are efficiently attained andsince certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention that, as amatter of language, might be said to fall therebetween.

1. An electro-mechanical energy conversion system to convert andtransfer energy from an input energy source to an output energy loadcomprising an energy converter device coupled between the input energysource and the output energy load to receive and to convert energy fromthe input energy source and to transfer the converted energy to theoutput energy load and an energy conversion and transfer controloperatively coupled to said energy converter device to control theconversion of energy from the input energy source and energy transfer tothe output energy load by said energy converter device in response to aplurality of predetermined conditions, said energy converter devicecomprising an energy converter section including a permanent magnetmachine having a rotor and stator to convert the energy from the inputenergy source and to selectively transfer the converted energy to theoutput energy load and an energy transfer section including a pluralityof stator control elements coupled to said stator and a plurality ofrotor control elements coupled to said rotor of said permanent magnetmachine, said plurality of stator control elements and said plurality ofrotor control elements operatively coupled by a resonant transfer linkto transfer energy between said stator and the rotor to control theoperation of said permanent magnet machine and wherein said energyconversion and transfer control comprises an energy converter control tocontrol the operation of said energy converter device and a source/loadcontrol to control the operation of the input energy source and outputenergy load with respect to said energy converter device wherein eachsaid stator energy transfer control element comprises a switch coupledto each phase of said stator of said permanent magnet machine.
 2. Theelectro-mechanical energy conversion system of claim 1 wherein the inputand output switches are programmed to operate as a charge pump toprovide a high switch sample rates to transfer charge at high power andhigh frequency and to charge pump sequence to provide the required inputto output voltage gain at the reduced PMG rotation rates.
 3. Theelectro-mechanical energy conversion system of claim 1 wherein the inputswitches from each phase is energized in a timed pattern so that thephase AC input is processed by charge transfer directly to acorresponding phase output thereby eliminating the rectification and DClink required with PWM conversion.
 4. The electro-mechanical energyconversion system of claim 1 wherein the input and the desired chargetransfer conditions to perform soft-start and rapid shut-down of currentflow.
 5. The electro-mechanical energy conversion system of claim 1wherein said resonant transfer link provides electrical isolation atabove and below said resonant transfer link resonating frequency andwhereby the control of the input switches and output switches are drivenwith a timing pattern and sequence to provide the volt-amps reactance tothe three phase load during the fault disturbance.
 6. Theelectro-mechanical energy conversion system of claim 1 wherein saidresonant transfer link is bi-directional.
 7. The electro-mechanicalenergy conversion system of claim 1 further includes an isolationelement is coupled between said plurality of stator control elements andsaid plurality of rotor control elements.
 8. The electro-mechanicalenergy conversion system of claim 7 wherein said isolation elementcomprises a transformer.
 9. The electro-mechanical energy conversionsystem of claim 6 wherein the energy transfer device further includes astator ground energy transfer control element and a second ground energytransfer control element coupled to ground on each side of saidbi-directional resonant transfer link.
 10. The electro-mechanical energyconversion system of claim 9 wherein said input switches are timesequenced is a timing pattern to allow each phase of the generator tosupply sinusoidal current at the desired generator power factor andsequencing the output switch to supply sinusoidal current at the powerfactor requested by the AC grid.
 11. The electro-mechanical energyconversion system of claim 1 wherein the voltage for each said statorenergy transfer control element and each said output phase isinterrogated to determine whether or not power for phases on said statorand for phases on said output are within a predetermined range of thepredetermined reference level.
 12. The electro-mechanical energyconversion system of claim 11 wherein when the initial charge V_(CS) isgreater than the output voltage E_(O), the input voltage E_(I) isconnected to the output voltage E_(O).